It could be a simple strain/muscle sprain.
It could be a bony trauma.
It could be referred pain from the heart (if it occurs after exertion)
it could be a blood vessel disease leading to decreased blood flow, local nerve injury, soft tissue tumor etc.
You would need to contact your physcian so that proper tests can be done to diagnose your condition,
If you need more information, just let me know. Do remember to
ACCEPT the reply, and consider giving a BONUS if you feel that it was useful,
regards
Dr. Gupta

